Electrical conductor



Jan. 12, 1932. R, w l s 1,840,377

ELECTRICAL CONDUCTOR Original Filed April 2, 1924 //v VEN 70H Hoar/T rH. W/LL/A/vs 9. WJM

A TTOHNEY Patented Jan. 12, 1932 UNITED STATES PATENT oFFIc ROBERT R.WILLIAMS, 0F ROSELLE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ELECTRICALCON DUGTOR briginal application filed April 2, 1924, Serial No. 703,660.Divided and this application filed June 2, 1988,

Serial No. 282,473, and'in This is a division of my application forpatent Serial No. 703,660, filed April 2, 192 1, which has issued asPatent No. 1,689,312 on ()ct..30, 1928.

This invention relates to electrical conductors and more particularly tothe insulated electrical conductors of submarine cables.

it is object of the invention to improve 10 the insulation of suchconductors both electrically and mechanically and to apply theinsulating material to the conductor in such a manner as not todeleteriously affect the conductor itself and in the case of a loadedconductor, to apply the insulating material so that the loading materialwith which the conductor is wrapped will notbe subject to injury.

The use of hard rubber or semi-hard rub- "ac her as the material forinsulating submarine conductors oilers important advantages because ofits low conductance, low dielectric constant and the fact that it ismore rigid than soft rubber and therefore its osmotic swelling by waterabsorption is very limited. However. it the rubber compound isvulcanized on the conductor it is very difiicult to prevent deformationof the insulation during the long vulcanizing process necessary and,furthermore, the extent of the sulphur attack on the conductor isobjectionable during the long period of heating. Moreover vulcanizationof the rubber compound on the conductor cannot be accomplished so as togive asatisfactory, result in the case of a continuously loadedconductor of the type recently developed. In this conductor, a recentlydiscovered alloy is employed for the loading material, such an alloyhaving a permeability at low magnetizing forces far in excess of thatobtained with the best iron wire heretofore employed for continuousloading. However, to obtain the best results with this new alloy whenused in a submarine cable, it is necessary to protect it from mechanicalstrains induced by hydrostatic pressure exerted on it at sea bottom andto protect against such strains it has been found desirable toimpregnate the loaded conductor with an insulating compound such asliquid Canada December 18, 1924.

bitumen that fills all the interstices between adjacent turns of theloading material and between the loading material and the conductoritself and also in the case of a stranded conductor between adjacentstrands of the conductor. To this end, it is preferable to employ animpregnating material which is fluid at the temperature encountered ingreat depths of water. Complete disclosures of the new loading materialand its application to submarine cable conductors are found in patentsto G. V. Elmen No. 1,586,884 and O. E. Buckley, Nos. 1,586,874: and1,586,875, all issued on June 1, 1926. It is not satisfactory tovulcanize the rubber compound on a core of this type in which a layer ofliquid bitumen is provided under the insulating material since theliquid bitumen mixes with the rubber compound during vulcanization andhardens to such an extent as to render it useless in protecting theloading material from subsequent strains.

To provide an insulated conductor having the desired characteristics,the invention contemplates the use of an insulating compound which isfirst vulcanized then rendered plastic and extruded in a continuoussheath about the conductor by means of heat and pressure.

In the accompanying drawings, Fig. 1 is a sectional view of an extrudingpress by means of which the plastic mass of prevulcanized rubber isextruded about the conductor, and Fig. 2 is a view of a continuouslloaded conductor made in accordance witli the features of thisinvention.

In practicing this invention, sheets of vulcanized hard rubber arerendered plastic by working them in standard rubber mills, the rolls ofwhich are heated, or in some other equivalent manner. The term hardrubber is here used to also include these compositions sometimesreferred to as semi-hard rubber in which the sulphur component may be aslow as 15 per cent. In order that the vulcanized sheets may be moreeasily rendered sufficiently plastic to permit the material beingextruded, it is desirable to include in the rubber compound athermoplastic material such as a bitumen, preferably of one of the' ispossible to use, in whole or in part,

harder varieties. While the composition of the insulating compound willobviously depend largely upon the temperatures and pressures employed acompound, which may be extruded at a temperature of 150 C. or somewhatless and with extruding pressures'of from 1000 to 2000 pounds per squareinch consists of approximately 60% rubber,

sulphur and 20% bitumen vulcanized attem- V thoroughly worked by theheated rolls of the mill, the plastic mass 3 is fed into the hopper W 4Lof the extrudmg'press shown 1n 1 1g. 1 or r the drawings. This press isprovided with a tubular central portion 5 into which the e trudingmaterial passes as it leaves the hopper, being forced along by means ofa rotating worm 6 driven by gear 7. The gear and worm are provided witha hollow central portion through which the conductor to be insulated isdriven at a predetermined rate by means not shown. emerges through theend of the worm 6, it

' passes through the compressed plastic mass and the die 9 helc inposition by a retaining plate 10 maintains the desired outer diameter ofthe insulated conductor. In oroer to main.-

' tain the insulating material in a plastic con- .dition until after itis extruded, the'press is provided with jackets 11, 11 through whichlive steam is passed from pipes 12, 12. A steam pressure is preferablymaintained so as to insure a suitable temperatureof approxi mately 150C. V

In Fig. 2 there is shown the finished conductor comprising a centralconducting core 15 surrounded by conductor strands 16, 16 about which ishelically wrapped the loading material 17 over which is placed a coatingoi liquid bitumen 18. The conductor completed thus far is passed throughthe truding press where it is provided with a sheath of pre vulcanizedinsulating compound.

' What is claimed is:

1. In combination, an electrical conductor and a continuous sheath ofinsulation mainly comprising thermoplastic vulcanized rubber surroundingsaid conductor. 2. An insulated electrical conductor com-- prising aconductor having a heavy layer of insulation forming a continuous sheathtightly enclosing said conductor and said insulation comprisingthermoplastic vulcan- As the conductor ized rubber and hard bitumen, therubber predominatin 3. A continuously loaded cable comprising aconductor having .applied thereabout a magneticinaterial in the form ofan elongated strand and filled with a semi-fluid in sulating materialand a heavy sheath of thermoplastic vulcanized rubber closelysurrounding the filled loaded conductor. 7

4:. An electrical-conductor, a magnetic material surrounding-saidconductor, a continuous sheath of vulcanized rubber around said magneticmaterialand a filling of pressure equalizing material of at leastsemi-liquid insulating material within said sheatln 5. A continuouslyloaded submarine cable comprising a conductor, a magnetic loadingmaterial forming a layer loosely surrounding said conductor, a fillingof semi-fluid bitumen adjacent to and filling the interstices under saidlayer of loading'material, a heavy sheath of thermoplastic vulcanigedrubber surrounding the filled loaded conductor, said sheath forming aseamless envelope in intimate contact with the bitumen. 6. Acontinuously loaded cable in accordance with claim 5 in which saidthermoplastic rubber contains about 20% of hard bitumen.

.7. A submarine cable comprising a conductor, a continuous layer ofmagnetic loading material surrounding said conductor, a continuousseamless sheath enveloping the loaded conductor, said sheath being ofrubber vulcanized to a hardness sufficient to preventabreakdown of itsinsulating'properties during a prolonged submergence in salt Water underseabottom conditions, and a filling within said sheath of a materialwhich remains semi-fluid when the cable is subjected to sea bottomtemperatures. 7 a r 8. A submarine cable comprising a conductor, acontinuous layer around said conductor of magnetic material having adesirable magnetic property which is deleteriously affected by strainsin the material, a seamless insulating sheath of vulcanized rubber ofsufficient hardness to prevent osmotic swelling in sea water, saidsheath being jointless

